Design of a High Voltage Lithium Ion Energy Storage System

One of the deliverables for the GM/DOE sponsored EcoCAR2 competition involved the design and validation of an energy storage system (ESS) that could withstand 20g of acceleration in the longitudinal direction, 20g of acceleration in the lateral direction, and 8g of acceleration in the vertical direction with a minimum safety factor of 2, in the event of a crash. Rose-Hulman Institute of Technology (RHIT) elected to base their energy storage system off of A123 battery modules (7×15s2p) and components. The design included a thermal analysis for various drive cycles and a mechanical analysis of the enclosure built to support and protect the battery modules. The thermal analysis investigated passive cooling versus active cooling and, after identifying active cooling as the best strategy, an appropriately sized cooling loop was developed. The mechanical analysis involved the use of Siemens NX7.5 to develop CAD models for the ESS enclosure components. These enclosure components included the battery base plate (interface that allows for module mounting), the battery casing (surrounds the modules) and the battery top plate (results in a completely contained system). The mechanical analysis of the ESS also required the use of NASTRAN to perform finite element analysis (FEA) on the module-to-base plate mounting and the pack-to-vehicle mounting. The pack-to-vehicle mounting was achieved by mounting the ESS to a subframe that will be welded into the vehicle.